Steering shaft

ABSTRACT

A coupling and sliding section A 3  is formed by an outer shaft A 1  and an inner shaft A 2  of a steering shaft A which is telescopically contractable in the axial direction during receipt of an impact. A resin material 5 is injected between a slid portion 4 of the inner shaft A 2  and a sliding portion 2 of the outer shaft A 1  through an opening 1a of the outer shaft A 1 , thereby forming a sliding resin portion 6. In addition, a fixing resin portion 6 is formed in the coupling and sliding section A 3  at an appropriate interval from the sliding resin portion 6.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a steering shaft in which a resin-coated layer is formed in a sliding portion and which has a sliding coupling for permitting smooth sliding, and to an apparatus for manufacturing the same.

2. Description of the Related Art

Conventionally, as shown in FIG. 15, a steering shaft is structured so that an axial end portion of an upper shaft U is fitted over an axial end portion of a lower shaft L by adopting a splined structure or an oval, straight-sided cross-sectional structure to form a fitted coupling section so as to allow the upper shaft U to be slidable in the axial direction, and that two injection-molded portions I formed of a synthetic resin are provided between the upper shaft U and the lower shaft U, respectively at an appropriate distance from each end of the fitted coupling section. The injection-molded portions I serve to prevent a clearance in the fitted coupling section of the steering shaft so as to allow the steering shaft of a steering system to be telescopically contractable to secure the safety of the driver during a collision of the vehicle.

A gap is prvided in the fitted coupling section between the lower shaft L and the upper shaft U so that the upper shaft U can be readily positioned or to be movable relative to the lower shaft L. When the lower shaft L and the upper shaft U are fitted, coupled, and fixed to each other by the injection-molded portions I, the injection-molded portions I must be so provided that their axes are concentrically aligned with each other as practically as possible.

However, discharge ports (air vents) are provided in rear surface portions of the upper shaft U (i.e., an outer shaft) in such a manner as to diametrically oppose respective injection ports and form pairs therewith, which oppose injection ports, so as to ensure that a molten synthetic resin, which is cured to form the injection-molded portions I, may be filled sufficiently in forming grooves formed in the lower shaft L (i.e., an inner shaft). For this reason, there are cases where the lower shaft L is pushed in one direction by the ijecting pressure of the molten resin acting in the same direction, so that the lower shaft L is offset within the upper shaft U, and the two shafts are fitted, coupled, and fixed to each other with the axes of the two shafts offset. In such a case, when a load in a bending direction acts on the steering shaft during a collision of the vehicle, there is the possibility of the contracting movement of the steering shaft becoming dull depending on the direction.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a steering shaft capable of undergoing stable and smooth contracting movement, thereby overcoming the above-described drawbacks of the conventional art.

Another object of the present invention is to provide an apparatus for manufacturing a steering wheel which makes it possible to manufacture a steering wheel capable of undergoing stable and smooth contracting movement.

To this end, in accordance with one aspect of the present invention, there is provided a steering shaft comprising: an inner shaft; an outer shaft coupled to and fitted over the inner shaft at a coupling and sliding section of the steering shaft in such a manner as to be telescopically retractable in an axial direction with respect to the inner shaft during the receipt of an impact; and a sliding resin portion formed by injecting a resin material between a slid portion of the inner shaft and a sliding portion of the outer shaft through an opening of the outer shaft.

In accordance with another aspect of the present invention, there is provided an apparatus for manufacturing a steering shaft, comprising: a mold provided with an outer shaft accommodating portion for accommodating an outer shaft of the steering shaft and an inner shaft accommodating portion for accommodating an inner shaft thereof, a molten-resin injection guide portion communicating with an opening of the outer shaft being formed in the inner shaft accommodating portion.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) is a side elevational view, partly in section, of a steering shaft in accordance with the present invention;

FIG. 1(B) is a side elevational view, partly in section, of a coupling and sliding section of the steering shaft;

FIG. 2 is a vertical side elevational view illustrating an injecting mold half and a supporting mold half of a mold for molding the steering shaft;

FIG. 3 is a cross-sectional view illustrating a state in which the coupling and sliding section is clamped by the injecting mold half and the supporting mold half;

FIG. 4 is a cross-sectional view illustrating a state in which a molten-resin injection guide portion communicates with an opening of an outer shaft;

FIG. 5 is a front vertical cross-sectional view of the injecting mold half, the supporting mold half, and an inner shaft;

FIG. 6 is a perspective view of the injecting mold half;

FIG. 7 is a plan view of the injecting mold half;

FIG. 8 is an enlarged view illustrating a state in which the molten-resin injection guide portion communicates with the opening of the outer shaft;

FIG. 9 is an enlarged front vertical cross-sectional view of the injecting mold half, the supporting mold half, and the inner shaft;

FIG. 10(A) is a cross-sectional view of another example of the coupling and sliding section;

FIG. 10(B) is a cross-sectional view taken in the direction of arrows along line I--I of FIG. 10(A);

FIG. 10C is a cross-sectional view taken in the direction of arrows along line II--II of FIG. 10(A);

FIG. 11(A) is a partially cross-sectional view of the coupling and sliding section in accordance with another embodiment;

FIG. 11(B) is an enlarged cross-sectional view of the opening of the outer shaft, shown in FIG. 11(A), and its vicinity;

FIG. 12(A) is a cross-sectional view, similar to FIG. 11(B), of a modification of the embodiment shown in FIGS. 11(A) and 11(B);

FIG. 12(B) is a cross-sectional view taken in the direction of arrows along line III--III of FIG. 12(A);

FIG. 13A is a side elevational view of the inner shaft in accordance with still another embodiment;

FIG. 13(B) is a cross-sectional view of the embodiment using the inner shaft shown in FIG. 13(A);

FIG. 14 is a cross-sectional view illustrating a modification of the embodiment shown in FIGS. 13(A) and 13(B); and

FIG. 15 is cross-sectional view of an injection-molded portion of a conventional steering wheel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, a description will be given of the embodiments of the present invention. As shown in FIG. 1(A), a steering shaft A is comprised of an outer shaft A₁ and an inner shaft A₂. The outer shaft A₁ is coupled to and fitted over the inner shaft A₂ in such a manner as to be telescopically retractable in its axial direction in sliding contact therewith, thereby forming a coupling and sliding section A₃. The coupling and sliding section A₃ undergoes a sliding operation only during the receipt of an impact, and absorbs the impact as the steering shaft A is shrunk in its axial direction when a vehicle undergoes a collision.

A sliding portion 2 is formed on an inner peripheral surface of the coupling and sliding section A₃ of the outer shaft A₁, i.e., on an inner peripheral surface of an end portion of an outer shaft body 1. Meanwhile, a slid portion 2 is formed on an outer peripheral surface of the inner shaft A₂, i.e., on an outer peripheral surface of an end portion of an inner shaft body 3. Specifically, splines are used for the sliding portion 2 and the slid portion 4, and sliding splines 2a and slid splines 4a engage each other, as shown in FIG. 3.

In practice, the steering shaft A is comprised of an upper shaft and a lower shaft, and, in the embodiment shown in FIGS. 1(A) and 1(B), the outer shaft A₁ is used as the upper shaft, while the inner shaft A₂ is used as the lower shaft. The arrangement provided is such that the inner shaft A₂ does not rotatively slip in the outer shaft A₁, and the outer shaft A₁ and the inner shaft A₂ always rotate integrally. As another example of each of the sliding portion 2 and the slid portion 4, not a circular shape but an oval, straight-sided shape in cross section may be used. For instance, the sliding portion 2 and the slid portion 4 may be constituted by an oval, straight-sided sliding portion 2b and an oval, straight-sided slid portion 4b, as shown in FIGS. 10(A) to 10(C). In addition, polygonal shapes, such as a hexagonal shape, or a substantially elliptical shape may be alternatively used.

The steering shaft A constituted by the outer shaft A₁ and the inner shaft A₂ telescopically contracts during the receipt of an impact, and a resin material 5 is filled between the sliding portion 2 and the slid portion 4, thereby forming a sliding resin portion 6 (see FIG. 1B). Specifically, the resin material 5 is filled between the sliding portion 2 on an opening 1a side of the outer shaft A₁ and an end portion of the slid portion 4 of the inner shaft A₂, and constiutes a fixing support by means of frictional resistance. When an impact of a fixed level or more is applied to the steering shaft A, and the steering shaft A contracts in the axial direction, even if the inner shaft A₂ is slightly bent with respect to the axial direction of the outer shaft A₁, the sliding resin portion 6 allows the outer shaft A₁ to slide smoothly in the axial direction, and makes it possible to prevent the inner shaft A₂ from biting at the outer shaft A₁.

Furthermore, as shown in FIGS. 1B and 2, a fixing annular groove 3a is formed on a peripheral surface of the slid portion 4 on an axially opposite side of the coupling and sliding section A₃ to the portion where the sliding resin portion 6 is formed with an appropriate interval therebetween. A fixing resin portion 8 (see FIG. 1B) having the function of a shear pin is formed in the fixing annular groove 3a by a fixing resin material 7 which is injected through an injection port 1b in the outer shaft A₁. By means of the fixing resin portion 8, the coupling and sliding section A₃ of the steering shaft A does not undergo the sliding operation until an impact of a fixed level or more is applied thereto.

Next, a description will be given of a method of forming the coupling and sliding section A₃ of the steering shaft A. As shown in FIG. 2, a mold C is comprised of an injecting mold half C₁ and a supporting mold half C₂. The steering shaft A constituted by the outer shaft A₁ and the inner shaft A₂ is disposed between the injecting mold half C₁ the supporting mold half C₂. At this time, the sliding portion 2 of the outer shaft A₁ and the slid portion 4 of the inner shaft A₂ are slidably coupled to each other.

As shown in FIGS. 2 and 3, the mold C is provided with outer shaft accommodating portions 12 for accommodating the outer shaft A₁ of the steering shaft A and inner shaft accommodating portions 13 for accommodating the inner shaft A₂. A molten-resin injection guide portion 14 communicating with the opening 1a of the outer shaft A₁ is formed in the inner shaft accommodating portion 13 of the injecting mold half C₁.

The outer shaft accommodating portions 12 and the inner shaft accommodating portions 13 are formed in both the injecting mold half C₁ and the supporting mold half C₂. An injecting-side outer shaft accommodating portion 12a and an injecting-side inner shaft accommodating portion 13a are formed in an injecting mold body 10 on the injecting mold half C₁ side, while a supporting-side outer shaft accommodating portion 12b and a supporting-side inner shaft accommodating portion 13b are formed in a supporting mold body 11 on the supporting mold half C₂ side (see FIG. 2).

The outer shaft accommodating portion 12 and the inner shaft accommodating portion 13 are distinguished from each other by a stepped portion where the diameter of the shaft changes (see FIGS. 2 and 6). As shown in FIGS. 3 to 5, the molten-resin injection guide portion 14 is formed in the injecting-side inner shaft accommodating portion 13a of the injecting mold half C₁, and the molten-resin injection guide portion 14 communicates with a molten-resin injection guide port 15.

The molten-resin injection guide port 15 is used to inject a molten resin material from outside the injecting mold half C₁. The molten-resin injection guide port 15 is structured such that, when the steering shaft A is accommodated in the mold C, the molten-resin injection guide port 15 communicates with the opening 1a of the outer shaft A₁, as shown in FIGS. 4, 7, and 8. When the molten resin material is injected through the molten-resin injection guide port 15, the molten resin material passes throuh the molten-resin injection guide portion 14, and enters the interior of the opening 1a of the outer shaft A₁ on the inner peripheral side thereof. A molten-resin injection guide port 16 for injecting the molten resin material which becomes the fixing resin material 7 is formed in the injeting mold half C₁.

The molten resin material which flows along the molten-resin injection guide portion 14 and into a gap between the outer shaft A₁ and the inner shaft A₂ through the opening 1a of the outer shaft A₁, as shown in FIG. 8, advances in such a manner as to fill the gap between the outer shaft A₁ and the inner shaft A₂.

At this time, as shown in FIG. 9, the coupling and sliding section A₃ of the outer shaft A₁ and the inner shaft A₂ is fixed by the injecting mold half C₁ and the supporting mold half C₂, so that the center O₂ of the inner shaft A₂ and the center O₁ of the outer shaft A₁ are aligned with each other (or substantially aligned with each other). For this reason, the inner shaft A₂ can be supported concentrically with the outer shaft A₁.

Next, a description will be given of another embodiment of the present invention.

In the embodiment shown in FIGS. 11(A) and 11(B), an annular groove 1c is provided in the inner peripheral surface of the outer shaft A₁ on the opening 1a side in an area where the resin material 5 is filled. This groove 1c is also filled with the resin material 5, thereby forming an annular holding projection 5a. In the arrangement in which this annular holding projection 5a is provided, the sliding resin portion 6, which is formed by injecting the resin material 5 between the slid portion 4 of the inner shaft A₂ and the sliding portion 2 of the outer shaft A₁ through the open end of the outer shaft A₁, is held between the shafts and is prevented from coming off, and the sliding characteristic of the outer shaft A₁ is improved.

FIGS. 12(A) and 12(B) show a modification of the embodiment shown in FIG. 11. In this modification, instead of providing the annular groove 1c, a pair of holding projectings 5a are formed by forming a pair of through holes 1d in the outer shaft A₁ on diametrically opposite sides thereof and by filling the through holes 1d with the resin material 5. This makes it possible to more effectively prevent the sliding resin portion 6 from coming off.

FIGS. 13(A) and 13(B) show still another embodiment in which an annular groove 3c is formed in an inner peripheral surface of the inner shaft A₂, and the groove 3c is filled with the resin material 5, thereby forming an annular holding projection 5a. In this embodiment, the sliding resin portion 6 is also prevented from coming off, and the annular holding projection 5a is sheared during sliding so as to secure the sliding characteristic between the shafts.

FIG. 14 is a modification of the embodiment shown in FIGS. 13A and 13B. In this modification, an enlarged-inside-diameter portion 1d is further provided at the opening 1a end of the outer shaft A₁, and the enlarged-inside-diameter portion 1d is also filled with the resin material 5. In this case, when the outer shaft A₁ slides, the sliding resin portion 6 formed by the resin material 5 is easily caught at the end of the outer shaft A₁, so that the outer shaft A₁ is capable of sliding while holding the sliding resin portion 6. Incidentally, it goes without saying that, in FIGS. 13(A), 13(B), and 14, it is possible to use holes instead of the annular groove 3c. In addition, the groove 3c may not be provided over the entire periphery and may be provided partially.

As described above, in the present invention, the steering shaft is structured such that, in the steering shaft A which is telescopically contractable in the axial direction, the sliding resin portion 6 is formed by injecting the resin material 5 between the slid portion 4 of the inner shaft A₂ and the sliding portion 2 of the outer shaft A₁ through the opening 1a of the outer shaft A₁ in the coupling and sliding section A₃ of the outer shaft A₁ and the inner shaft A₂. Accordingly, various advantages are offered in that, firstly, the axial movement of the outer shaft A₁ relative to the inner shaft A₂ in the coupling and sliding section A₃ can be made stable and smooth, that, secondly, even when a force in the bending direction has acted on the inner shaft during a collision, the movement of the outer shaft can be guided in the axial direction to ensure a stable operation, and that, thirdly, the coupling and sliding section A₃ can be guided and supported stably and firmly.

To give a more detailed description of the above advantages, in a first arrangement of the steering wheel in accordance with the present invention, the sliding resin portion 6 is formed in the coupling and sliding section A₃ by injecting the resin material 5 between the slid portion 4 of the inner shaft A₂ and the sliding portion 2 of the outer shaft A₁ through the opening 1a of the outer shaft A₁. If the resin material 5 is thus injected through the opening 1a of the outer shaft A₁, the molten resin material 5 advances substantially uniformly on the inner peripheral side of the outer shaft A₁ and is then cured, so that the inner shaft A₂ can be maintained and fixed concentrically with the outer shaft A₁.

For this reason, the axial movement of the outer shaft A₁ relative to the inner shaft A₂ in the coupling and sliding section A₃ is stable and smooth. In particular, since the molten resin material 5 which flows through the opening 1a side of the outer shaft A₁ is formed as the sliding resin portion 6, the sliding resin portion 6 is capable of preventing the inner shaft A₂ from biting at the outer shaft A₁.

In another arrangement, the coupling and sliding section A₃ of the outer shaft A₁ and th inner shaft A₂ in the steering shaft A which is telescopically contractable in the axial direction during receipt of an impact, the sliding resin portion 6 is formed by injecting the resin material 5 between the slid portion 4 of the inner shaft A₂ and the sliding portion 2 of the outer shaft A₁ through the opening 1a of the outer shaft A₁, and the fixing resin portion 8 is formed on an axially opposite side of the coupling and sliding section A₃ to the position where the sliding resin portion 6 is formed, at an appropriate interval therebetween. Consequently, since the fixing resin portion 8 is formed at an appropriate interval from the sliding resin portion 6, it is possible to improve the durability until an impact of a fixed level acts on the coupling and sliding section A₃, and to prevent an erroneous operation. The other advantages of this arrangement are similar to those of the first arrangement described above.

In still another arrangement, the steering wheel is arranged such that the sliding portion 2 and the slid portion 4 of the coupling and sliding section A₃ are provided with a splined structure. Since the sliding portion 2 and the slid portion 4 have the splined structure, the fitting accuracy improves, and the telescopic action can be made smooth. The other advantages of this arrangement are similar to those of the first arrangement described above.

In a further arrangement, the sliding portion 2 of the outer shaft A₁ and the slid portion 4 of the inner shaft A₂ in the coupling and sliding section A₃ are provided with noncircular cross sections, respectively. Since the outer shaft A₁ and the inner shaft A₂ in the coupling and sliding section A₃ are made noncircular in their cross sections, the structures of the sliding portion 2 and the slid portion 4 of the coupling and sliding section A₃ can be made very simple. At the same time, their telescopic action can be secured by the resin material 5. The other advantages of this arrangement are similar to those of the first arrangement described above.

In addition, the apparatus for manufacturing a steering shaft comprises: the mold C provided with the outer shaft accommodating portion 12 for accommodating the outer shaft A₁ of the steering shaft A and the inner shaft accommodating portion 13 for accommodating the inner shaft A₂ thereof, the molten-resin injection guide portion 14 communicating with the opening 1a of the outer shaft A₁ being formed in the inner shaft accommodating portion 13. Consequently, it is possible to form the coupling and sliding section A₃ of the steering shaft A very easily and efficiently.

To give a more detailed description of the advantages of the apparatus for manufacturing a steering wheel, when the molten resin is allowed to flow through the injection port of the mold C, the molten resin flows through the molten-resin injection guide portion 14 and is directed to the opening 1a of the outer shaft A₁, and is filled substantially uniformly on the inner periphery of the outer shaft A₁. Hence, the axial positions of the outer shaft A₁ and the inner shaft A₂ are made substantially concentric with each other, thereby making it possible to form the coupling and sliding section A₃ which undergoes favorable sliding movement during receipt of an impact. 

What is claimed is:
 1. A steering shaft comprising:an inner shaft including an inner shaft body and a slid portion, said inner shaft body having a diameter smaller than that of said slid portion; an outer shaft coupled to and fitted over said inner shaft at a coupling and sliding section of said steering shaft in such a manner as to be telescopically retractable in an axial direction with respect to said inner shaft during the receipt of an impact, said inner shaft body being disposed in such a manner as to extend into an opening at an axial end face portion of said outer shaft; and a sliding resin portion formed in such a manner as to extend axially into and coextensive with said opening defined by said axial end face of said outer shaft by injecting a resin material between said inner shaft body and a sliding portion of said outer shaft, said sliding resin portion being fixed in the axial direction of said outer shaft and supporting said inner shaft body in the opening at the axial end face portion of said outer shaft.
 2. A steering shaft according to claim 1, wherein the slid portion and the sliding portion of said coupling and sliding section have a splined structure.
 3. A steering shaft according to claim 1, wherein the sliding portion of said outer shaft and the slid portion of said inner shaft in said coupling and sliding section are provided with noncircular cross sections, respectively.
 4. A steering shaft comprising:an inner shaft including an inner shaft body and a slid portion, said inner shaft body having a diameter smaller than that of said slid portion; an outer shaft coupled to and fitted over said inner shaft at a coupling and sliding section of said steering shaft in such a manner as to be telescopically retractable in an axial direction with respect to said inner shaft during the receipt of an impact, said inner shaft body being disposed in such a manner as to extend into an opening at an axial end face portion of said outer shaft; and a sliding resin portion formed in such a manner as to extend axially into and coextensive with said opening defined by said axial end face of said outer shaft by injecting a resin material between said inner shaft body and a sliding portion of said outer shaft through the opening at the axial end face portion of said outer shaft, said sliding resin portion being fixed in the axial direction of said outer shaft and supporting said inner shaft body in the opening at the axial end face portion of said outer shaft.
 5. A steering shaft comprising:an inner shaft including an inner shaft body and a slid portion, said inner shaft body having a diameter smaller than that of said slid portion; an outer shaft coupled to and fitted over said inner shaft at a coupling and sliding section of said steering shaft in such a manner as to be telescopically retractable in an axial direction with respect to said inner shaft during the receipt of an impact, said inner shaft body being disposed in such a manner as to extend into an opening at an axial end face portion of said outer shaft; a sliding resin portion formed in such a manner as to extend axially into and coextensive with said opening defined by said axial end face of said outer shaft by injecting a resin material between said inner shaft body and a sliding portion of said outer shaft, said sliding resin portion being fixed in the axial direction of said outer shaft and supporting said inner shaft body in the opening at the axial end face portion of said outer shaft, and a fixing resin portion formed in said coupling and sliding section at a position axially opposite to a position where said sliding resin portion is formed, with an appropriate interval therebetween.
 6. A steering shaft comprising:an inner shaft including an inner shaft body and a slid portion, said inner shaft body having a diameter smaller than that of said slid portion; an outer shaft coupled to and fitted over said inner shaft at a coupling and sliding section of said steering shaft in such a manner as to be telescopically retractable in an axial direction with respect to said inner shaft during the receipt of an impact, said inner shaft body being disposed in such a manner as to extend into an opening at an axial end face portion of said outer shaft; a sliding resin portion formed in such a manner as to extend axially into and coextensive with said opening defined by said axial end face of said outer shaft by injecting a resin material between said inner shaft body and a sliding portion of said outer shaft, said sliding resin portion being fixed in the axial direction of said outer shaft and supporting said inner shaft body in the opening at the axial end face portion of said outer shaft, and a holding projection formed on said sliding resin portion.
 7. A steering shaft according to claim 6, wherein said holding projection is formed on an outer shaft side.
 8. A steering shaft according to claim 6, wherein said holding projection is formed on an inner shaft side and is provided in such a manner as to be sheared when said inner shaft slides.
 9. A steering shaft comprising:an inner shaft including an inner shaft body and a slid portion, said inner shaft body having a diameter smaller than that of said slid portion; an outer shaft coupled to and fitted over said inner shaft at a coupling and sliding section of said steering shaft in such a manner as to be telescopically retractable in an axial direction with respect to said inner shaft during the receipt of an impact, said inner shaft body being disposed in such a manner as to extend into an opening at an axial end face portion of said outer shaft; a sliding resin portion formed in such a manner as to extend axially into and coextensive with said opening defined by said axial end face of said outer shaft by injecting a resin material between said inner shaft body and a sliding portion of said outer shaft, said sliding resin portion being fixed in the axial direction of said outer shaft and supporting said inner shaft body in the opening at the axial end face portion of said outer shaft, a holding projection formed on said sliding resin portion; and a fixing resin portion formed in said coupling and sliding section at a position axially opposite to a position where said sliding resin portion is formed, with an appropriate interval therebetween.
 10. A steering shaft comprising:an inner shaft including an inner shaft body and a slid portion, said inner shaft body having a diameter smaller than that of said slid portion; an outer shaft coupled to and fitted over said inner shaft at a coupling and sliding section of said steering shaft in such a manner as to be telescopically retractable in an axial direction with respect to said inner shaft during the receipt of an impact, said inner shaft body being disposed in such a manner as to extend into an opening at an axial end face portion of said outer shaft; and a sliding resin portion formed in such a manner as to extend axially into and coextensive with said opening defined by said axial end face of said outer shaft by injecting a resin material into a space defined by an outer periphery of said inner shaft body, an inner periphery of a sliding portion of said outer shaft, and a plane of the opening, said sliding resin portion being fixed in the axial direction of said outer shaft and supporting said inner shaft body in the opening at the axial end face portion of said outer shaft.
 11. A steering shaft according to claim 10, wherein said coupling and sliding section has a splined structure, and said sliding resin portion is formed by injecting the resin material into a space defined by the outer periphery of said inner shaft body, the inner periphery of the sliding portion of said outer shaft, an inclined end face of each spline at the opening, and the plane of the opening.
 12. A steering shaft comprising:an inner shaft including an inner shaft body and a slid portion, said inner shaft body having a diameter smaller than that of said slid portion; an outer shaft coupled to and fitted over said inner shaft at a coupling and sliding section of said steering shaft in such a manner as to be telescopically retractable in an axial direction with respect to said inner shaft during the receipt of an impact, said inner shaft body being disposed in such a manner as to extend into an opening at an axial end face portion of said outer shaft; a sliding resin portion formed in such a manner as to extend axially into and coextensive with said opening defined by said axial end face of said outer shaft by injecting a resin material into a space defined by an outer periphery of said inner shaft body, an inner periphery of a sliding portion of said outer shaft, and a plane of the opening, said sliding resin portion being fixed in the axial direction of said outer shaft and supporting said inner shaft body in the opening at the axial end face portion of said outer shaft, and a holding projection formed on said sliding resin portion.
 13. A steering shaft comprising:an inner shaft including an inner shaft body and a slid portion, said inner shaft body having a diameter smaller than that of said slid portion; an outer shaft coupled to and fitted over said inner shaft at a coupling and sliding section of said steering shaft in such a manner as to be telescopically retractable in an axial direction with respect to said inner shaft during the receipt of an impact, said inner shaft body being disposed in such a manner as to extend into an opening at an axial end face portion of said outer shaft; a sliding resin portion formed in such a manner as to extend axially into and coextensive with said opening defined by said axial end face of said outer shaft by injecting a resin material into a space defined by an outer periphery of said inner shaft body, an inner periphery of a sliding portion of said outer shaft, and a plane of the opening, said sliding resin portion being fixed in the axial direction of said outer shaft and supporting said inner shaft body in the opening at the axial end face portion of said outer shaft, and a fixing resin portion formed on an axially opposite side of said coupling and sliding section to a position where said sliding resin portion is formed, with a predetermined interval therebetween.
 14. A steering shaft comprising:an inner shaft including an inner shaft body and a slid portion, said inner shaft body having a diameter smaller than that of said slid portion; an outer shaft coupled to and fitted over said inner shaft at a coupling and sliding section of said steering shaft in such a manner as to be telescopically retractable in an axial direction with respect to said inner shaft during the receipt of an impact, said inner shaft body being disposed in such a manner as to extend into an opening at an axial end face portion of said outer shaft; a sliding resin portion formed in such a manner as to extend axially into and coextensive with said opening defined by said axial end face of said outer shaft by injecting a resin material into a space defined by an outer periphery of said inner shaft body, an inner periphery of a sliding portion of said outer shaft, and a plane of the opening, said sliding resin portion being fixed in the axial direction of said outer shaft and supporting said inner shaft body in the opening at the axial end face portion of said outer shaft; a holding projection formed on said sliding resin portion, and a fixing resin portion formed on an axially opposite side of said coupling and sliding section to a position where said sliding resin portion is formed, with a predetermined interval therebetween. 